1. Field of the Invention
The present invention relates to an optical assembly that installs a light-emitting device or a light-receiving device therein, in particular, relates to a structure for enhancing the tolerance against the electro-static discharge.
2. Related Prior Art
The conventional structure of an optical assembly (hereinafter denoted as OSA) comprises a CAN-type package for installing a light-emitting or light-receiving device and an alignment member including a plurality of cylindrical members connected to the head portion of the CAN package. The CAN package, so called as a co-axial package, including a disk-shaped stem and a cap, both made of metal, mounts the light-emitting device such as laser diode onto the stem so as to coincide the optical axis of the laser diode with the center axis of the cylindrical members. The head portion of the cap provides a lens for concentrating the light emitted from the laser diode.
For such CAN-type package with the laser diode, the cylindrical members align and optically couple the laser diode with the distal end of an optical fiber. That is, the plurality of cylindrical members aligns the optical axis of the laser diode in the XY plane, which intersecting the optical axis, and along the Z-direction parallel to the optical axis. Here, the optical axis means a virtual line connecting the laser diode with the distal end of the optical fiber. After the alignment, the cylindrical members are welded not only to each other but also to the CAN package in order to secure the optical coupling permanently. An optical transceiver completes to install such OSAs therein and to connect these OSAs to the electronic circuit provided on a circuit board.
In the conventional OSA, fixing of the cylindrical members to each other or to the CAN package used to be carried out with the YAG laser welding. In the YAG laser welding, optical beams output from the YAG laser with extreme power are irradiated in short time to points to be welded to melt there locally. In order to melt locally with the optical beam, the members to be welded are limited to materials with low thermal conductivity in addition to the mechanical stiffness. Therefore, metals such as iron (Fe), stainless steel, and Kovar™, are applied the cylindrical member.
On the other hand, the OSA is installed within the transceiver as the cylindrical member thereof protrudes into the optical receptacle of the transceiver. Here, the optical receptacle is formed in the front side of the optical transceiver and receives an optical connector to couple the optical fiber secured in the optical connector with the laser diode in the CAN package. In this arrangement, since the cylindrical member made of metal is exposed outside of the transceiver, the cylindrical member may operate as an antenna to import noise from the outside or to export the noise to the outside as an electromagnetic interference (EMI). Moreover, the optical connector with the static charge mates with the OSA in the receptacle, this static charge is conveyed to the circuit board installed in the transceiver via the metal OSA, which may break the circuit element mounted thereon.
To make the OSA with resin, in particular, a portion of the cylindrical member thereof, will solve at least above subject. However, the resin sleeve tends to be affected by the abrasion due to the ferrule inserting there into or extracting therefrom. Moreover, since the resin sleeve is inferior in holding the ferrule therein to the metal sleeve, the resin sleeve is unsuitable to the single mode fiber having a relatively small core.